Modified polysaccharides containing amphiphilic hydrocarbon moieties

ABSTRACT

Modified polysaccharides (such as starches, gums, chitosans, celluloses, alginates, sugars, etc.), which are commonly used in the paper industry as strengthening agents, surface sizes, coating binders, emulsifiers and adhesives, can be combined into a single molecule with amphiphilic hydrocarbons (e.g. surface active agents) which are commonly utilized in the paper industry to control absorbency, improve softness, enhance surface feel and function as dispersants. The resulting molecule is a modified polysaccharide having surface active moieties which can provide several potential benefits, depending on the specific combination employed, including: (a) strength aids that do not impart stiffness; (b) softeners that do not reduce strength; (c) wet strength with improved wet/dry strength ratio; (d) debonders with reduced linting and sloughing; (e) strength aids with controlled absorbency; and (f) surface sizing agents with improved tactile properties.

This application is a continuation of U.S. Ser. No. 09/488,429,now U.S.Pat. No. 6,517,678, titled “Modified Polysaccharides ContainingAmphiphilic Hydrocarbon Moieties” filed on Jan. 20, 2000, whichapplication claims priority from U.S. Ser. No. 60/117,085 entitled“Modified Polysaccharides Containing Amphiphilic Hydrocarbon Moieties”filed on Jan. 25, 1999, now abandoned. The entirety of U.S. Ser. No.09/488,429 is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

In the manufacture of paper products, such as facial tissue, bathtissue, paper towels, dinner napkins and the like, a wide variety ofproduct properties are imparted to the final product through the use ofchemical additives. Examples of such additives include softeners,debonders, wet strength agents, dry strength agents, sizing agents,opacifiers and the like. In many instances, more than one chemicaladditive is added to the product at some point in the manufacturingprocess. Unfortunately, there are instances where certain chemicaladditives may not be compatible with each other or may be detrimental tothe efficiency of the papermaking process, such as can be the case withthe effect of wet end chemicals on the downstream efficiency of crepingadhesives. Another limitation, which is associated with wet end chemicaladdition, is the limited availability of adequate bonding sites on thepapermaking fibers to which the chemicals can attach themselves. Undersuch circumstances, more than one chemical functionality compete for thelimited available bonding sites, oftentimes resulting in theinsufficient retention of one or both chemicals on the fibers.

Therefore, there is a need for a means of applying more than onechemical functionality to a paper web which mitigates the limitationscreated by limited number of bonding sites.

SUMMARY OF THE INVENTION

In certain instances, two or more chemical functionalities can becombined into a single molecule, such that the combined molecule impartsat least two distinct product properties to the final paper product thatheretofore have been imparted through the use of two or more differentmolecules. More specifically, modified polysaccharides (such asstarches, gums, chitosans, celluloses, alginates, sugars, etc.), whichare commonly used in the paper industry as strengthening agents, surfacesizes, coating binders, emulsifiers and adhesives, can be combined intoa single molecule with amphiphilic hydrocarbons (e.g. surface activeagents) which are commonly utilized in the paper industry to controlabsorbency, improve softness, enhance surface feel and function asdispersants. The resulting molecule is a modified polysaccharide havingsurface active moieties which can provide several potential benefits,depending on the specific combination employed, including: (a) strengthaids that do not impart stiffness; (b) softeners that do not reducestrength; (c) wet strength with improved wet/dry strength ratio; (d)debonders with reduced linting and sloughing; (e) strength aids withcontrolled absorbency; and (f) surface sizing agents with improvedtactile properties.

Hence in one aspect, the invention resides in a modified polysaccharidecontaining one or more amphiphilic hydrocarbon moieties, said modifiedpolysaccharide having the following structure:

Polysac-Z₃R₁

or

—Polysac—Z₃R₁—Polysac—

where

Polysac=any polysaccharide, monosaccharide, or sugar residue, modifiedor unmodified;

Z₃=—CH₂, —COO—, —OOC—, —CONH—, —NHCO—, —O—, —S—, —OSO₂O—, —OCOO—,—NHCOO—,

—OOCNH, —NHCONH—, —CONCO—, or any other radical capable of bridging theR₁ group to the polysaccharide backbone portion of the molecule; and

R₁=any organofunctional group with the only limitation being that R₁must contain a moiety consisting of an amphiphilic hydrocarbon, normalor branched, saturated or unsaturated, substituted or unsubstituted,with or without esterification, with or without etherification, with ourwithout sulfonation, with or without hydroxylation, with or withoutethoxylation or propoxylation, and having a carbon chain length of 4 orgreater.

In another aspect, the invention resides in a paper sheet, such as atissue or towel sheet, comprising a modified polysaccharide containingone or more amphiphilic hydrocarbon moieties, said modifiedpolysaccharide having the following structure:

Polysac—Z₃R₁

or

—Polysac—Z₃R₁—Polysac—

where

Polysac=any polysaccharide, monosaccharide, or sugar residue, modifiedor unmodified;

Z₃=—CH₂, —COO—, —OOC—, —CONH—, —NHCO—, —O—, —S—, —OSO₂O—, —OCOO—,—NHCOO—, —OOCNH, —NHCONH—, —CONCO—, or any other radical capable ofbridging the R₁ group to the polysaccharide backbone portion of themolecule; and

R₁=any organofunctional group with the only limitation being that R₁must contain a moiety consisting of an amphiphilic hydrocarbon, normalor branched, saturated or unsaturated, substituted or unsubstituted,with or without esterification, with or without etherification, with ourwithout sulfonation, with or without hydroxylation, with or withoutethoxylation or propoxylation, and having a carbon chain length of 4 orgreater.

In another aspect, the invention resides in a method of making a papersheet, such as a tissue or towel sheet, comprising the steps of: (a)forming an aqueous suspension of papermaking fibers; (b) depositing theaqueous suspension of papermaking fibers onto a forming fabric to form aweb; and (c) dewatering and drying the web to form a paper sheet,wherein a modified polysaccharide is added to the aqueous suspension,said modified polysaccharide having the following structure:

Polysac—Z₃R₁

or

—Polysac—Z₃R₁—Polysac—

where

Polysac=any polysaccharide, monosaccharide, or sugar residue, modifiedor unmodified;

Z₃=—CH₂, —COO—, —OOC—, —CONH—, —NHCO—, —O—, —S—, —OSO₂O—, —OCOO—,—NHCOO—, —OOCNH, —NHCONH—, —CONCO—, or any other radical capable ofbridging the R₁ group to the polysaccharide backbone portion of themolecule; and

R₁=any organofunctional group with the only limitation being that R₁must contain a moiety consisting of an amphiphilic hydrocarbon, normalor branched, saturated or unsaturated, substituted or unsubstituted,with or without esterification, with or without etherification, with ourwithout sulfonation, with or without hydroxylation, with or withoutethoxylation or propoxylation, and having a carbon chain length of 4 orgreater.

The amount of the modified polysaccharide added to the fibers can befrom about 0.02 to about 2 weight percent, on a dry fiber basis, morespecifically from about 0.05 to about 1 weight percent, and still morespecifically from about 0.1 to about 0.75 weight percent. The modifiedpolysaccharide can be added to the fibers at any point in thepapermaking process. A preferred addition point is where the fibers aresuspended in water. However, modified polysaccharides can also be addedtopically to a dried paper web.

As used herein, polysaccharides are carbohydrates that can be hydrolyzedto many monosaccharides and include, but are not limited to, starches(primarily modified starches from potato, corn, waxy maize, tapioca andwheat) which can be unmodified, acid modified, enzyme modified,cationic, anionic or amphoteric; carboxymethylcellulose, modified orunmodified; natural gums, modified or unmodified (such as from locustbean and guar); sugars, modified or unmodified; chitosan, modified orunmodified; and dextrins, modified and unmodified. “Monosaccharide” is acarbohydrate that cannot be hydrolyzed into simpler compounds.“Carbohydrates” are polyhydroxy aldehydes, polyhydroxy ketones orcompounds that can be hydrolyzed to them.

As used herein, amphiphilic hydrocarbon moieties are organic compoundsincluding alkanes, alkenes, alkynes and cyclic aliphatics which containsurface active agents. The amphiphilic hydrocarbons can be linear orbranched, saturated or unsaturated, substituted or unsubstituted.

Methods of making paper products which can benefit from the variousaspects of this invention are well known to those skilled in thepapermaking art. Exemplary patents include U.S. Pat. No. 5,785,813issued Jul. 28, 1998 to Smith et al. entitled “Method of Treating aPapermaking Furnish For Making Soft Tissue”; U.S. Pat. No. 5,772,845issued Jun. 30, 1998 to Farrington, Jr. et al. entitled “Soft Tissue”;U.S. Pat. No. 5,746,887 issued May 5, 1998 to Wendt et al. entitled“Method of Making Soft Tissue Products”; and U.S. Pat. No. 5,591,306issued Jan. 7, 1997 to Kaun entitled “Method For Making Soft TissueUsing Cationic Silicones”, all of which are hereby incorporated byreference.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a macroscopic structure of amphiphilic moieties attached inpendant fashion to a polysaccharide.

FIG. 2 shows a macroscopic structure of amphiphilic moieties attached inseries to a polysaccharide molecule.

DETAILED DESCRIPTION OF THE INVENTION

To further describe the invention, examples of the synthesis of some ofthe various chemical species are given below.

Polysaccharides

Starches

Unmodified starch has the structure as shown below. Unmodified starchescan differ in properties such as amylopectin: amylose ratio, granuledimension, gelatinization temperature, and molecular weight. Unmodifiedstarches have very little affinity for fibers, and modifications arewidely done to extend the number of wet end starch additives availablefor use. Modifications to starches generally fall under one of thefollowing categories: 1) Physical modifications, 2) Fractionation intoamylose and amylopectin components, 3) Thermomechanical conversion, 4)Acid hydrolysis, 5) Chemical modifications, 6) Oxidation, 7)Derivatization and 8) Enzyme conversion.

Starch derivatives are the most common type of dry strength additiveused in the paper industry. The 1990 edition of the TAPPI publication“Commercially Available Chemical Agents for Paper and PaperboardManufacture” lists 27 different starch dry strength products. Starchchemistry primarily centers on reactions with the hydroxyl groups andthe glucosidic (C—O—C) linkages. Hydroxyl groups being subject tostandard substitution reactions and the glucosidic linkages beingsubject to cleavage. In theory the primary alcohol at the C-6 positionshould be more reactive than the secondary alcohols at the C-2 and C-3positions. Also, it has been found that the tuber starches are morereactive than the cereal starches.

A large variety of starch esters and ethers have been described. Fewhave been actively marketed due to non-specific properties resultingfrom the substitution groups. Esters will generally be prepared viareaction of the acid chloride or anhydride with the starch. Hydrophobictype structures can be introduced with this functionalization and suchstructures have found applications in the paper industry as adhesives,and grease resistant paper size coatings. (Starch Conversion Technology,1985)

Cationic starches are recognized as the choice for wet end additives dueto their substantivity with cellulose fibers. The cationization ofstarches is accomplished by reaction with various tertiary andquaternary amine reagents. In general, a reactive chloride or epoxygroup on one end of the reagent reacts with a starch hydroxyl group. Thecationic portion of the amine then ionizes in the presence of water toform the positively charged derivative which is substantive to fiber.Quaternary ammonium derivatives are most commonly used in the paper.

Other ionic charged starches are produced by reaction of starch withamino, imino, ammonium, sulfonium, or phosphonium groups, all of whichcarry an ionic charge. The key factor in their usefulness is theiraffinity for negatively charged substrates such as cellulose. Theseionic starches have found widespread use in the paper industry as wetend additives, surface sizing agents and coating binders. Cationicstarches improve sheet strength by promoting ionic bonding andadditional hydrogen bonding within the cellulose fibers. Some commonreagents used to prepare cationic starches include: 2-diethylaminoethylchloride (DEC); 2-dimethylaminoethyl chloride; 2-diisopropylaminoethylchloride; 2-diethylaminoethyl bromide; 2-dimethylaminoisopropylchloride; N-alkyl N-(2-haloethyl)-aminomethylphosphonic acids; and2,3-epoxypropyltrimethylammonium chloride.

Epichlorohydrin reacts with tertiary amines or their salts in water ornonaqueous solvents to form the quaternary ammonium reagents.Trimethylamine, dimethylbenzyl amine, triethylamine, N-ethyl andN-methyl morpholine, dimethylcyclohexylamine, and dimethyldodecylamine(Paschall, E.F., U.S. Pat. No. 2,876,217, 1959 and U.S. Pat. No.2,995,513, 1961) have been used.

Cyanamide and dialkyl cyanamides can be used to attach imino carbamategroups on starches. These groups show cationic activity upon treatmentwith acids. The acidified products are stable to hydrolysis. Cationiccyanamide starches show useful properties as textile sizes and drystrength additives in paper. (Chamberlain, R. J., U.S. Pat. No.3,438,970, 1969)

Aminoethylated starches are produced by treatment of ethyleneimine withstarch in organic solvents or dry. Acidified products are useful as wetend paper additives (Hamerstrand, et al, “An evaluation of cationicaminoethyl cereal flours as wet end paper additives” Tappi, 58, 112,1975). Starches react with isatoic anhydride and its derivatives to formanthranilate esters with primary or secondary amino groups (U.S. Pat.Nos. 3,449,886; 3,511,830; 3,513,156; 3,620,913). Products with primaryamino anthranilate groups can be derivatized and used to improve wet rubresistance in paper coatings.

Cationic starches containing anionic xanthate groups provided both wetstrength and dry strength to paper when used as wet end additives inunbleached kraft pulp systems. (Powers, et al, U.S. Pat. No. #3,649,624,1972). In this system it is believed that the permanent wet strengthresults from covalent bonding from the xanthate side chain reactions.(Cheng, W. C., et al, Die Starke, 30, 280, 1978) Cationic dialdehydestarches are useful wet end additives for providing temporary wetstrength to paper. They are produced by periodic acid oxidation oftertiary amino or quatemary ammonium starches, by treating dialdehydestarch with hydrazine or hydrazide compounds containing tertiary aminoor quaternary ammonium groups, and several other reactions.

Graft copolymers of starch are widely known. Some graft copolymers madewith starches include: vinyl alcohol; vinyl acetate; methylmethacrylate; acrylonitrile; styrene; acrylamide; acrylic acid;methacrylic acid; and cationic monomers with amino substituentsincluding: 2-hydroxy-3-methacrylopropyltrimethylammonium chloride(HMAC); N,N-dimethylaminoethyl methacrylate, nitric acid salt(DMAEMA*HNO₃); N-t-butylaminoethyl methacrylate, nitric acid salt(TBAEMA*HNO₃); andN, N,N-trimethylaminoethyl methacrylate methyl sulfate(TMAEMA*MS).

Polyacrylonitrile (PAN)/starch graft copolymers are well known in theart. Treatment of the PAN/starch graft copolymers with NaOH or KOHconverts the nitrile substituents to a mixture of carboxamide and alkalimetal carboxylate. Such hydrolyzed starch-g-PAN polymers (HSPAN) areused as thickening agents and as water absorbents. Importantapplications for HSPAN include use in disposable soft goods designed toabsorb bodily fluids. (Lindsay, W. F., Absorbent Starch BasedCopolymers—Their Characteristics and Applications, Formed FabricsIndustry, 8(5), 20, 1977).

Copolymers with water-soluble grafts are also well known. Many of thewater soluble graft copolymers are used for flocculation and flotationof suspended solids in the paper, mining, oil drilling and otherindustries. (Burr, R. C., et al, “Starch Graft Copolymers for WaterTreatment”, Die Starke, 27, 155, 1975). Graft copolymers from thecationic amine containing monomers are effective retention aids in themanufacture of filled papers. Starch-g-poly(acrylamide-co-TMAEMA*MS) wasfound to improve drainage rates while increasing dry tensile strength ofunfilled paper handsheets. (Heath, H. D., et al, “Flocculatingagent-starch blends for interfiber bonding and filler retention,comparative performance with cationic starches”, TAPPI, 57(11), 109,1974.)

Thermoplastic-g-starch materials are also known, primarily with acrylateesters, methacrylate esters and styrene. Primary interest for thesematerials is in preparation of biodegradable plastics. No use of thesematerials as a paper additive has been found.

Other miscellaneous graft copolymers are known. Saponifiedstarch-g-poly(vinyl acetate) has been patented as a sizing agent forcotton, rayon and polyester yarns. (Prokofeva, et al, Russian patent451731, 1975). Graft copolymers have been saponified to convertstarch-g-poly(vinyl acetate) copolymers into starch-g-poly(vinylacetate) copolymers. As with the thermoplastic-g-starch copolymers mostof these materials have been evaluated as polymeric materials in theirown right and not as additives for paper.

Carboxymethyl cellulose, methylcellulose, alginate, and animal glues aresuperior film formers. These materials are typically applied via surfaceapplication and not added in the wet end of the process to improve drystrength. The products are relatively expensive and although they can beused alone they are typically employed in conjunction with starches orother materials.

Gums:

Gums and mucilages use in papermaking dates back to ancient China. Thesemucilages were obtained from various plant roots and stems and were usedprimarily as deflocculating and suspending agents for the long fiberedpulps. As papermaking evolved other advantages of using these materialsbecame obvious including the ability of these materials to hold the wetfiber mat together during the drying process. As papermaking evolved tousing shorter and shorter fibers these gums found increased use as ameans of obtaining paper strength. Since World War II the use of gums inpapermaking has increased substantially.

Water soluble, polysaccharide gums are highly hydrophilic polymershaving chemical structures similar to cellulose. The main chain consistsof β-1,4 linked mannose sugar units with occurrence of α-1,6 linkedgalactose side chains. Their similarity to cellulose means they arecapable of extensive hydrogen bonding with fiber surfaces. Furtherenhancement of dry strength occurs due to the linear nature of themolecules.

They are vegetable gums and include as examples 1) locust bean gum, 2)guar gum, 3) tamarind gum, and 4) karaya, okra and others. Locust beangum and guar gum are the most commonly used. They have been used in thepaper industry since just prior to WWII. Since the natural materials arenon-ionic they are not retained on fibers to any great extent. Allsuccessful commercial products have cationic groups attached to the mainchain which increases the retention of the gums on the fiber surfaces.Typical addition rates for these materials are on the order of0.1-0.35%.

The dry strength improvement of paper furnishes through use ofpolysaccharide gums is derived from the linear nature of the polymer andthrough hydrogen bonding of the hydroxyl hydrogen of the polymer withsimilar functional groups on the surface of the cellulosic fibers.

The most effective gums are quaternary ammonium chloride derivativescontaining a cationic charge. The cationic functionality will help thegum retain better to the fibers as well as reducing the usually highernegative zeta potential of the paper furnish, especially when fillersand fines are present in the white water. This change in zeta potentialleads to a more thorough agglomeration of the fines in the system byforming more cohesive flocs. These in turn are trapped by longer fibersfilling the voids among the larger fibers with additional material thathelps in the inter fiber bonding of the wet web, which in turn leads todry strength improvement.

Although a variety of guar gum derivatives have been prepared, there areonly three dervivatizations which have achieved commercial significance.These are 1) Quaternization, 2) Carboxymethylation and 3)Hydroxypropylation. The structure of guar gum and derivatives is shownbelow.

Chitosan:

Chitosan is a high molecular weight linear carbohydrate composed ofβ-1,4-linked 2-amino-2-deoxy-D-glucose units. It is prepared from thehydrolysis of the N-acetyl derivative called chitin. Chitin is isolatedin commercial quantities from the shells of crustaceans. Chitin isinsoluble in most common solvents, however, chitosan is soluble inacidified water due to the presence of basic amino groups. Depending onthe source and degree of deacetylation chitosans can vary in molecularweight and in free amine content. In sufficiently acidic environmentsthe amino groups become protonated and chitosan behaves as a cationicpolyelectrolyte. It has been reported that chitosans increase the drystrength of paper more effectively than other common papermakingadditives including the polyethylenimines and polyacrylamides.

Chitosan and starch are both polymers of D-glucose but differ in twoaspects. First, chitosan has an amino group on each glucose unit andtherefore has a stronger cationic character than cationic starch.Secondly, starch differs in its molecular. configuration. Starchcontains amylopectin which has a three dimensional molecular structureand amylose, which has linear macromolecules. The glucose molecules ofstarch have an α-configuration which gives the molecules a helical form.Chitosan resembles cellulose and xylans in that it has β-linkedD-monosaccharide units and tends to have straight molecular chains. Thefunctionally reactive groups of a straight polymer molecule are moreeasily accessible than those of a branched, random configurationmolecule and are expected to interact more effectively with the polargroups on cellulose. The structure of chitosan is shown below.

Sugars

Also included in the saccharides are the simple sugars. These includethe hexoses shown below. These compounds actually exist in the cyclicacetal form as shown below for glucose. Derivatives of these sugars areincluded within this definition.

Such derivatives include but are not limited to things such as gluconicacid, mucic acid, mannitol, sorbitol, etc. The derivatives generally donot exist in cyclic form.

Amphiphilic Hydrocarbon Moieties

Amphiphilic hydrocarbon moieties are a group of surface active agents(surfactants) capable of modifying the interface between phases.Surfactants are widely used by the industry for cleaning (detergency),solubilizing, dispersing, suspending, emulsifying, wetting and foamcontrol. In the papermaking industry, they are often used for deinking,dispersing and foam control. They have an amphiphilic molecularstructure: containing at least one hydrophilic (polar) region and atleast one lipophilic (non-polar, hydrophobic) region within the samemolecule. When placed in a given interface, the hydrophilic end leanstoward the polar phase while the lipophilic end orients itself towardthe non polar phase.

The hydrophilic end can be added to a hydrophobe synthetically to createthe amphiphilic molecular structure. The following is a schematicpathway for making a variety of surfactants:

Based on the charge, surfactants can be grouped as amphoteric, anionic,cationic and nonionic.

First with regard to the amphoteric surfactants, the charges on thehydrophilic end change with the environmental pH: positive in acidic pH,negative at high pH and become zwitterions at the imtermediate pH.Surfactants included in this category include alkylamido alkyl aminesand alkyl substituted amino acids.

Structure commonly shared by alkylamido alkyl amines:

where

R₀=a C₄ or higher alkyl or aliphatic hydrocarbon, normal or branched,saturated or unsaturated, substituted or unsubstituted.

n≧2

R₁=hydroxy or carboxy ended alkyl or hydroxyalkyl groups, C chain≧2C,with or without ethoxylation, propoxylation or other substitution.

Z=H or other cationic counterion.

Structure shared commonly by alkyl substituted amino acids:

R₁—NR′₂Z

where

R₁=alkyl or aliphatic hydrocarbon, normal or branched, saturated orunsaturated, substituted or unsubstituted, C chain≧4C,

n≧2,

Z=H or other cationic counterion

R′=carboxylic end of the amino acid.

With regard to the anionics, the hydrophilic end of the surfactantmolecule is negatively charge. Anionics consist of five major chemicalstructures: acylated amino acids/acyl peptides, carboxylic acids andsalts, sulfonic acid derivatives, sulfuric acid derivatives andphosphoric acid derivatives.

Structure commonly shared by acylated amino acids and acyl peptides:

R₀OCO—R₁—COOZ

or

HOOC—R₁—COOZ

where

R₀=alkyl or aliphatic hydrocarbon, normal or branched, saturated orunsaturated, substituted or unsubstituted, C chain≧4C,

R₁=alkyl substituted amino acid moiety; or —NH—CHX—CO)_(n)—NH—CHX—

where n≧1, X=amino acid sidechain; or alkyl—NHCOR′ where R′=aliphatichydrocarbon, normal or branched, saturated or unsaturated, substitutedor unsubstituted, C chain≧4C

Z=H or other cationic counterion

Structure commonly shared by carboxylic acid and salts:

R—COOZ

where:

R=alkyl or aliphatic hydrocarbon, normal or branched, saturated orunsaturated, substituted or unsubstituted, with or withoutesterification, with or without etherification, C chain≧4C.

Z=H or other cationic counterion

Structure commonly shared by sulfonic acid derivatives:

RCO—NR₁—(CH₂)_(n)—SO₃Z

or

alkyl aryl-SO₃Z

or

R—SO₃Z

or

ROOC—(CH₂)_(n)—CH SO₃—COOZ

or

[RCO—NH—(OCH₂)_(n)—OOC—CH SO₃—COO]2Z

or

R(OCH₂CH₂)_(n)—SO₃Z

where

R=alkyl or aliphatic hydrocarbon, normal or branched, saturated orunsaturated, substituted or unsubstituted, with or withoutesterification, with or without etherification, with or withoutsulfonation, with or without hydroxylation, C chain≧4C;

R₁=alkyl or hydroxy alkyl, C chain≧1C;

n≧1;

Z=H or other counterion.

Structure commonly shared by sulfuric acid derivatives:

R—OSO₃Z

where

R=aliphatic hydrocarbon, normal or branched, saturated or unsaturated,substituted or unsubstituted, with or without esterification, with orwithout etherification, with or without sulfonation, with or withouthydroxylation, with or without ethoxylation or propoxylation, C chain≧4C

Z=H or other counterion.

Structure commonly shared by phosphoric acid derivatives:

R—OPO₃Z

where

R=aliphatic hydrocarbon, normal or branched, saturated or unsaturated,substituted or unsubstituted, with or without esterification, with orwithout etherification, with or without sulfonation, with or withouthydroxylation, with or without ethoxylation or propoxylation, C chain≧4C

Z=H or other counterion.

With regard to the cationics, these are surfactants with a positivelycharged nitrogen atom on the hydrophobic end. The charge may bepermanent and non pH dependent (such as quaternary ammonium compounds)or pH dependent (such as cationic amines). They include alkylsubstituted ammonium salts, heterocyclic ammonium salts, alkylsubstituted imidazolinium salts and alkyl amines.

Structure commonly shared by this group:

N⁺R₄Z⁻

where:

R=H, alkyl, hydroxyalkyl, ethoxylated and/or propoxylation alkyl,benzyl, or aliphatic hydrocarbon, normal or branched, saturated orunsaturated, substituted or unsubstituted, with or withoutesterification, with or without etherification, with or withoutsulfonation, with or without hydroxylation, with or withoutcarboxylation, with or without ethoxylation or propoxylation, C chain≧4C

Z=H or other counterion.

With regard to the nonionics, in this group the molecule has no charge.The hydrophilic end often contains a polyether (polyoxyethylene) or oneor more hydroxyl groups. They generally include alcohols, alkylphenols,esters, ethers, amine oxides, alkylamines, alkylamides, polyalkyleneoxide block copolymers.

Modified polysaccharides Containing Amphiphilic Hydrocarbons

Two primary methods are envisioned for incorporating amphiphilicmoieties into the polysaccharide based materials. In the first schemethe amphiphilic moieties are added via reaction between a functionalgroup on the polysaccharide and a second functional group attached tothe reagent containing the amphiphilic moiety. The polysaccharides maybe derivatized or non-derivatized, cationic or non-cationic. The generalreaction scheme is defined as follows:

Polysac—Z₁+Z₂—R₁→Polysac—Z₃R₁

where:

Z₁=functional group attached to the polysaccharide molecule and may bepresent either from the natural state or from a derivatization process.Examples of Z₁ functional groups include but are not limited to —H,—NH₂, COOH, —CH₂X (X=halogen), —CN, —CHO, —CS₂.

Z₂=Functional group attached to the R₁ moiety whose purpose is to reactwith a Z₁ functional group thereby attaching the R₁ moiety covalently tothe polysaccharide.

Z₃=Bridging ligand formed as a result of reaction of Z₁ with Z₂.

R₁=any organofunctional group with the only limitation being that R₁must contain a moiety consisting of an amphiphilic hydrocarbon, normalor branched, saturated or unsaturated, substituted or unsubstituted,with or without esterification, with or without etherification, with ourwithout sulfonation, with or without hydroxylation, with or withoutethoxylation or propoxylation, C chain≧4 carbons.

Such materials in general will have a macroscopic structure as shown inFIG. 1 where the amphiphilic moieties are attached in a pendant fashionto the polysaccharide. Where decreased water solubility becomes an issuea second moiety, containing only a hydrophyllic portion may be attachedto the polysaccharide. Examples of such materials would include ethyleneglycol and its oligomers and polymers.

In theory the Z₂—R₁ reactant could be difunctional of the form Z₂—R₂—Z₂,however, in the case of high molecular weight polysaccharides thiscrosslinking could lead to water insoluble products, suitable forcoatings but not useful for wet end applications.

Synthesis of modified polysaccharides similar to those in FIG. 1 couldbe prepared via a number of methods. Attachment of the amphiphilichydrocarbon moiety could be achieved via the following paths:

(1) Modified cationic polysaccharides prepared via reaction with one ofthe following or similar reagents:

Where R₁, R₂, R₃ are any alkyl groups, chosen such that at least one ofR₁, R₂, or R₃ is an amphiphilic hydrocarbon, normal or branched,saturated or unsaturated, substituted or unsubstituted, with or withoutesterification, with or without etherification, with our withoutsulfonation, with or without hydroxylation, with or without ethoxylationor propoxylation, C chain≧4 carbons.

(2) Dialdehyde polysaccharides, particularly dialdehyde starches,cationic or non-cationic, modified with fatty acid groups via reactionof the aldehyde groups with alcohols, amines, sulfinic acids,sulfyhydryl compounds and the like containing a linear or branched,saturated or unsaturated, substituted or non-substituted C₈ or higheraliphatic hydrocarbon moiety.

Ethoxylated fatty acid derivatives of the form:

HO—CH₂CH₂O)_(n)R₆

where R₆ is an organofunctional radical containing a linear or branched,saturated or unsaturated, substituted or non-substituted C₈ or higheraliphatic hydrocarbon moiety, can be used to directly incorporateamphiphilic functionality onto the polysaccharide backbone as shownbelow.

(3) Direct reaction of a functionalized linear or branched, saturated orunsaturated, substituted or non-substituted amphiphilic hydrocarbonmoiety with the hydroxyl or amine groups on the polysaccharide. Anexample of such a reaction is shown below for chitosan:

(4) Graft polymerization of hydrophobic and or hydrophilic units ontothe polysaccharide backbone. Modified vinyl monomers are capable ofbeing grafted onto polysaccharide backbones as has been demonstrated forvarious starches. Use of modified vinyl monomers such as:

where:

R₂=H, C₁₋₄ alkyl.

R₄=Z₂—R6 where:

Z₂=Ar, CH₂, COO—, CONH—, —O—, —S—, OSO₂O—, —CONHCO—, —CONHCHOHCHOO—, anyradical capable of bridging the R₆ group to the vinyl backbone portionof the molecule.

R6=any aliphatic, linear or branched, saturated or unsaturated,substituted or non-substituted amphiphilic hydrocarbon.

In the second scheme the amphiphilic hydrocarbon moieties are added viareaction between a functional group on the polysaccharide and a secondfunctional group attached to the reagent containing the amphiphilichydrocarbon moiety, however in this case two functional groups areattached to amphiphilic hydrocarbon containing reagent. Thepolysaccharides may be derivatized or non-derivatized, cationic ornon-cationic. The general reaction scheme is defined as follows:

Polysac'Z₁+Z₂—R₁—Z₂→—Polysac—Z₃R₁—Polysac—

where:

Z₁=functional group attached to the polysaccharide molecule and may bepresent either from the natural state or from a derivatization process.Examples of Z₁ functional groups include but is not limited to —OH,—NH2, —COOH, —CH₂X (X=halogen), —CN, —CHO, —CS₂.

Z₂=Functional group attached to the R₁ moiety whose purpose is to reactwith a Z₁ functional group thereby attaching the R₁ moiety covalently tothe polysaccharide.

R₁=any organofunctional group with the only limitation being that R₁must contain a moiety consisting of a saturated or unsaturated,substituted or unsubstituted, linear or branched amphiphilichydrocarbon.

Such materials in general will have a macroscopic structure as shown inFIG. 2.

In theory the polysaccharides could be of high molecular weight,however, the crosslinking would be expected to lead to water insolubleproducts, suitable perhaps for coatings but not useful for wet endapplications. For wet end applications, lower molecular weightpolysaccharides including the oligomers as well as the monosaccharidesare better candidates for this approach.

Synthesis of modified polysaccharides similar to those in FIG. 2 couldbe prepared via a number of methods. A few specific examples follow:

1) Reaction with diacids or diacid halides of the formula:

where:

Z=OH, halogen, other displaceable group.

Y=any residue chosen such that Y contains an amphiphilic moiety.

The displaceable groups on the reactants can react with either primary—OH or —NH2 groups on the saccharide to form the corresponding ester oramide.

2) Reaction between dialdehyde polysaccharides, cationic or non-cationicand residues chosen from the group of difunctional amphiphilichydrocarbons where these residues are incorporated into thepolysaccharide via reaction with the aldehyde groups on the starch. Anexample is shown below.

It will be appreciated that the foregoing examples, given for purposesof illustration, shall not be construed as limiting the scope of thisinvention, which is defined by the following claims and all equivalentsthereto.

We claim:
 1. A method of making a paper sheet comprising the steps of: (a) forming an aqueous suspension of papermaking fibers; (b) depositing the aqueous suspension of papermaking fibers onto a forming fabric to form a web; and (c) dewatering and drying the web to form a paper sheet, wherein a modified polysaccharide is added to the aqueous suspension, said modified polysaccharide having the following structure: —Polysac—Z₃R₁—Polysac— where Polysac=a polysaccharide, monosaccharide or sugar residue; Z₃=a bridging radical which serves to attach the R₁ group to the Polysac residue; and R₁=an organofunctional group containing a moiety consisting of an amphiphilic hydrocarbon having a carbon chain length of 4 or greater.
 2. The method of claim 1 wherein the bridging radical is selected from the group consisting of —CH₂, —COO—, —OOC—, —CONH—, —NHCO—, —O—, —S—, —OSO₂O—, —OCOO—, —NHCOO—, —OOCNH, —NHCONH— and —CONCO—.
 3. A paper sheet comprising a modified polysaccharide containing one or more amphiphilic hydrocarbon moieties, said modified polysaccharide having the following structure: —Polysac—Z₃R₁—Polysac— where Polysac=a polysaccharide, monosaccharide or sugar residue; Z₃=a bridging radical which serves to attach the R₁ group to the Polysac residue; and R₁=an organofunctional group containing a moiety consisting of an amphiphilic hydrocarbon having a carbon chain length of 4 or greater.
 4. The paper sheet of claim 3 wherein the bridging radical is selected from the group consisting of —CH₂, —COO—, —OOC—, —CONH—, —NHCO—, —O—, —S—, —OSO₂O—, —OCOO—, —NHCOO—, —OOCNH, —NHCONH— and —CONCO—. 